Modification of temporary database pages

ABSTRACT

A temporary page is allocated in which pages are loaded into main memory and having associated physical disk storage. The temporary page is also flagged as being temporary. Subsequently, a savepoint is initiated for the database so that, during the savepoint, the temporary page can be modified without acquiring a consistent change while preventing other non-temporary pages from being modified. Later, the savepoint can be finalized to enable the database to be rolled back to a point in time corresponding to the savepoint as part of a recovery process.

TECHNICAL FIELD

The current subject matter is directed to advanced database techniques in which temporary pages can be modified in parallel to savepoint operations.

BACKGROUND

Savepoints define points in time at which database transactions can be rolled back without affecting any operations that were performed prior to such savepoint. Modifications to pages stored within databases need to be synchronized relative to savepoints using consistent changes to guarantee data consistency after a restart of a database.

SUMMARY

In a first aspect, a temporary page is allocated in which pages are loaded into main memory and having associated physical disk storage. The temporary page is also flagged as being temporary. Subsequently, a savepoint is initiated for the database so that, during the savepoint, the temporary page can be modified without acquiring a consistent change while preventing other non-temporary pages from being modified. Later, the savepoint can be finalized to enable the database to be rolled back to a point in time corresponding to the savepoint as part of a recovery process.

The flagging can be performed prior to the initiation of the savepoint. Alternatively, the flagging can be performed subsequent to the initiation of the savepoint.

The flagging of the temporary page can include flagging a control block associated with the temporary page indicating that it is temporary. The control block can be a transient object that is loaded into the main memory and not physically persisted in the associated physical disk storage. The temporary page can be automatically deleted after a restart of the database system.

The temporary page can be flushed to the associated physical disk storage when an amount of free memory in the main memory is below a pre-defined level.

The temporary page can be allocated by temp-pageaccess.

Non-transitory computer program products (i.e., physically embodied computer program products) are also described that store instructions, which when executed by one or more data processors of one or more computing systems, cause at least one data processor to perform operations herein. Similarly, computer systems are also described that may include one or more data processors and memory coupled to the one or more data processors. The memory may temporarily or permanently store instructions that cause at least one processor to perform one or more of the operations described herein. In addition, methods can be implemented by one or more data processors either within a single computing system or distributed among two or more computing systems. Such computing systems can be connected and can exchange data and/or commands or other instructions or the like via one or more connections, including but not limited to a connection over a network (e.g., the Internet, a wireless wide area network, a local area network, a wide area network, a wired network, or the like), via a direct connection between one or more of the multiple computing systems, etc.

The details of one or more variations of the subject matter described herein are set forth in the accompanying drawings and the description below. Other features and advantages of the subject matter described herein will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a system diagram illustrating an example database system for use in connection with the current subject matter;

FIG. 2 is a system diagram illustrating an example database system that can support distribution of server components across multiple hosts for scalability and/or availability purposes for use in connection with the current subject matter;

FIG. 3 is a diagram illustrating an architecture for an index server for use in connection with the current subject matter;

FIG. 4 is a process flow diagram illustrating allocation of temporary pages in an in-memory database system that can be modified during a savepoint; and

FIG. 5 is a diagram illustrating a sample computing device architecture for implementing various aspects described herein.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The current subject matter is directed to techniques for allocating temporary pages in an in-memory database system that can be modified without affecting/in parallel with a savepoint. Such an arrangement is advantageous in that it increases the overall performance of such a database.

FIG. 1 is a diagram 100 illustrating a database system 105 that can be used to implement aspects of the current subject matter. The database system 105 can, for example, be an in-memory database in which all relevant data is kept in main memory so that read operations can be executed without disk I/O and in which disk storage is required to make any changes durables. The database system 105 can include a plurality of servers including, for example, one or more of an index server 110, a name server 115, and/or an application services server 120. The database system 105 can also include one or more of an extended store server 125, a database deployment infrastructure (DDI) server 130, a data provisioning server 135, and/or a streaming cluster 140. The database system 105 can be accessed by a plurality of remote clients 145, 150 via different protocols such as SQL/MDX (by way of the index server 110) and/or web-based protocols such as HTTP (by way of the application services server 120).

The index server 110 can contain in-memory data stores and engines for processing data. The index server 110 can also be accessed by remote tools (via, for example, SQL queries), that can provide various development environment and administration tools. Additional details regarding an example implementation of the index server 110 is described and illustrated in connection with diagram 300 of FIG. 3.

The name server 115 can own information about the topology of the database system 105. In a distributed database system, the name server 115 can know where various components are running and which data is located on which server. In a database system 105 with multiple database containers, the name server 115 can have information about existing database containers and it can also hosts the system database. For example, the name server 115 can manage the information about existing tenant databases. Unlike a name server 115 in a single-container system, the name server 115 in a database system 105 having multiple database containers does not store topology information such as the location of tables in a distributed database. In a multi-container database system 105 such database-level topology information can be stored as part of the catalogs of the tenant databases.

The application services server 120 can enable native web applications used by one or more remote clients 150 accessing the database system 105 via a web protocol such as HTTP. The application services server 120 can allow developers to write and run various database applications without the need to run an additional application server. The application services server 120 can also be used to run web-based tools 155 for administration, life-cycle management and development. Other administration and development tools 160 can directly access the index server 110 for, example, via SQL and other protocols.

The extended store server 125 can be part of a dynamic tiering option that can include a high-performance disk-based column store for very big data up to the petabyte range and beyond. Less frequently accessed data (for which is it non-optimal to maintain in main memory of the index server 110) can be put into the extended store server 125. The dynamic tiering of the extended store server 125 allows for hosting of very large databases with a reduced cost of ownership as compared to conventional arrangements.

The DDI server 130 can be a separate server process that is part of a database deployment infrastructure (DDI). The DDI can be a layer of the database system 105 that simplifies the deployment of database objects using declarative design time artifacts. DDI can ensure a consistent deployment, for example by guaranteeing that multiple objects are deployed in the right sequence based on dependencies, and by implementing a transactional all-or-nothing deployment.

The data provisioning server 135 can provide enterprise information management and enable capabilities such as data provisioning in real time and batch mode, real-time data transformations, data quality functions, adapters for various types of remote sources, and an adapter SDK for developing additional adapters.

The streaming cluster 140 allows for various types of data streams (i.e., data feeds, etc.) to be utilized by the database system 105. The streaming cluster 140 allows for both consumption of data streams and for complex event processing.

FIG. 2 is a diagram 200 illustrating a variation of the database system 105 that can support distribution of server components across multiple hosts for scalability and/or availability purposes. This database system 105 can, for example, be identified by a single system ID (SID) and it is perceived as one unit from the perspective of an administrator, who can install, update, start up, shut down, or backup the system as a whole. The different components of the database system 105 can share the same metadata, and requests from client applications 150 can be transparently dispatched to different servers 110 ₁₋₃, 120 ₁₋₃, in the system, if required.

As is illustrated in FIG. 2, the distributed database system 105 can be installed on more than one host 210 ₁₋₃. Each host 210 ₁₋₃ is a machine that can comprise at least one data processor (e.g., a CPU, etc.), memory, storage, a network interface, and an operation system and which executes part of the database system 105. Each host 210 ₁₋₃ can execute a database instance 220 ₁₋₃ which comprises the set of components of the distributed database system 105 that are installed on one host 210 ₁₋₃. FIG. 2 shows a distributed system with three hosts, which each run a name server 110 ₁₋₃, index server 120 ₁₋₃, and so on (other components are omitted to simplify the illustration).

FIG. 3 is a diagram 300 illustrating an architecture for the index server 110 (which can, as indicated above, be one of many instances). A connection and session management component 302 can create and manage sessions and connections for the client applications 150. For each session, a set of parameters can be maintained such as, for example, auto commit settings or the current transaction isolation level.

Requests from the client applications 150 can be processed and executed by way of a request processing and execution control component 310. The database system 105 offers rich programming capabilities for running application-specific calculations inside the database system. In addition to SQL, MDX, and WIPE, the database system 105 can provide different programming languages for different use cases. SQLScript can be used to write database procedures and user defined functions that can be used in SQL statements. The L language is an imperative language, which can be used to implement operator logic that can be called by SQLScript procedures and for writing user-defined functions.

Once a session is established, client applications 150 typically use SQL statements to communicate with the index server 110 which can be handled by a SQL processor 312 within the request processing and execution control component 310. Analytical applications can use the multidimensional query language MDX (MultiDimensional eXpressions) via an MDX processor 322. For graph data, applications can use GEM (Graph Query and Manipulation) via a GEM processor 316, a graph query and manipulation language. SQL statements and MDX queries can be sent over the same connection with the client application 150 using the same network communication protocol. GEM statements can be sent using a built-in SQL system procedure.

The index server 110 can include an authentication component 304 that can be invoked with a new connection with a client application 150 is established. Users can be authenticated either by the database system 105 itself (login with user and password) or authentication can be delegated to an external authentication provider. An authorization manager 306 can be invoked by other components of the database system 105 to check whether the user has the required privileges to execute the requested operations.

Each statement can processed in the context of a transaction. New sessions can be implicitly assigned to a new transaction. The index server 110 can include a transaction manager 344 that coordinates transactions, controls transactional isolation, and keeps track of running and closed transactions. When a transaction is committed or rolled back, the transaction manager 344 can inform the involved engines about this event so they can execute necessary actions. The transaction manager 344 can provide various types of concurrency control and it can cooperate with a persistence layer 346 to achieve atomic and durable transactions.

Incoming SQL requests from the client applications 150 can be e received by the SQL processor 312. Data manipulation statements can be executed by the SQL processor 312 itself. Other types of requests can be delegated to the respective components. Data definition statements can be dispatched to a metadata manager 306, transaction control statements can be forwarded to the transaction manager 344, planning commands can be routed to a planning engine 318, and task related commands can forwarded to a task manager 324 (which can be part of a larger task framework) Incoming MDX requests can be delegated to the MDX processor 322. Procedure calls can be forwarded to the procedure processor 314, which further dispatches the calls, for example to a calculation engine 326, the GEM processor 316, a repository 300, or a DDI proxy 328.

The index server 110 can also include a planning engine 318 that allows planning applications, for instance for financial planning, to execute basic planning operations in the database layer. One such basic operation is to create a new version of a data set as a copy of an existing one while applying filters and transformations. For example, planning data for a new year can be created as a copy of the data from the previous year. Another example for a planning operation is the disaggregation operation that distributes target values from higher to lower aggregation levels based on a distribution function.

The SQL processor 312 can include an enterprise performance management (EPM) runtime component 320 that can form part of a larger platform providing an infrastructure for developing and running enterprise performance management applications on the database system 105. While the planning engine 318 can provide basic planning operations, the EPM platform provides a foundation for complete planning applications, based on by application-specific planning models managed in the database system 105.

The calculation engine 326 can provide a common infrastructure that implements various features such as SQLScript, MDX, GEM, tasks, and planning operations. The SQLScript processor 312, the MDX processor 322, the planning engine 318, the task manager 324, and the GEM processor 316 can translate the different programming languages, query languages, and models into a common representation that is optimized and executed by the calculation engine 326. The calculation engine 326 can implement those features using temporary results 340 which can be based, in part, on data within the relational stores 332.

Metadata can be accessed via the metadata manager component 306. Metadata, in this context, can comprise a variety of objects, such as definitions of relational tables, columns, views, indexes and procedures. Metadata of all these types can be stored in one common database catalog for all stores. The database catalog can be stored in tables in a row store 336 forming part of a group of relational stores 332. Other aspects of the database system 105 including, for example, support and multi-version concurrency control can also be used for metadata management. In distributed systems, central metadata is shared across servers and the metadata manager component 306 can coordinate or otherwise manage such sharing.

The relational stores 332 form the different data management components of the index server 110 and these relational stores can, for example, store data in main memory. The row store 336, a column store 338, and a federation component 334 are all relational data stores which can provide access to data organized in relational tables. The column store 338 can stores relational tables column-wise (i.e., in a column-oriented fashion, etc.). The column store 338 can also comprise text search and analysis capabilities, support for spatial data, and operators and storage for graph-structured data. With regard to graph-structured data, from an application viewpoint, the column store 338 could be viewed as a non-relational and schema-flexible in-memory data store for graph-structured data. However, technically such a graph store is not a separate physical data store. Instead it is built using the column store 338, which can have a dedicated graph API.

The row store 336 can stores relational tables row-wise. When a table is created, the creator can specify whether it should be row or column-based. Tables can be migrated between the two storage formats. While certain SQL extensions are only available for one kind of table (such as the “merge” command for column tables), standard SQL can be used on all tables. The index server 110 also provides functionality to combine both kinds of tables in one statement (join, sub query, union).

The federation component 334 can be viewed as a virtual relational data store. The federation component 334 can provide access to remote data in external data source system(s) 354 through virtual tables, which can be used in SQL queries in a fashion similar to normal tables.

The database system 105 can include an integration of a non-relational data store 342 into the index server 110. For example, the non-relational data store 342 can have data represented as networks of C++ objects, which can be persisted to disk. The non-relational data store 342 can be used, for example, for optimization and planning tasks that operate on large networks of data objects, for example in supply chain management. Unlike the row store 336 and the column store 338, the non-relational data store 342 does not use relational tables; rather, objects can be directly stored in containers provided by the persistence layer 346. Fixed size entry containers can be used to store objects of one class. Persisted objects can be loaded via their persisted object IDs, which can also be used to persist references between objects. In addition, access via in-memory indexes is supported. In that case, the objects need to contain search keys. The in-memory search index is created on first access. The non-relational data store 342 can be integrated with the transaction manager 344 to extends transaction management with sub-transactions, and to also provide a different locking protocol and implementation of multi version concurrency control.

An extended store is another relational store that can be used or otherwise form part of the database system 105. The extended store can, for example, be a disk-based column store optimized for managing very big tables, which ones do not want to keep in memory (as with the relational stores 332). The extended store can run in an extended store server 125 separate from the index server 110. The index server 110 can use the federation component 334 to send SQL statements to the extended store server 125.

The persistence layer 346 is responsible for durability and atomicity of transactions. The persistence layer 346 can ensure that the database system 105 is restored to the most recent committed state after a restart and that transactions are either completely executed or completely undone. To achieve this goal in an efficient way, the persistence layer 346 can use a combination of write-ahead logs, undo and cleanup logs, shadow paging and savepoints. The persistence layer 346 can provide interfaces for writing and reading persisted data and it can also contain a logger component that manages a recovery log. Recovery log entries can be written in the persistence layer 346 (in recovery log volumes 352) explicitly by using a log interface or implicitly when using the virtual file abstraction. The recovery log volumes 352 can include redo logs which specify database operations to be replayed whereas data volume 350 contains undo logs which specify database operations to be undone as well as cleanup logs of committed operations which can be executed by a garbage collection process to reorganize the data area (e.g. free up space occupied by deleted data etc.).

The persistence layer 346 stores data in persistent disk storage 348 which, in turn, can include data volumes 350 and/or recovery log volumes 352 that can be organized in pages. Different page sizes can be supported, for example, between 4k and 16M. Data can be loaded from the disk storage 348 and stored to disk page wise. For read and write access, pages can be loaded into a page buffer in memory. The page buffer need not have a minimum or maximum size, rather, all free memory not used for other things can be used for the page buffer. If the memory is needed elsewhere, least recently used pages can be removed from the cache. If a modified page is chosen to be removed, the page first needs to be persisted to disk storage 348. While the pages and the page buffer are managed by the persistence layer 346, the in-memory stores (i.e., the relational stores 332) can access data within loaded pages.

As noted above, the data volumes 350 can include a data store that together with undo and cleanup log and recovery log volumes 352 comprise the recovery log. Other types of storage arrangements can be utilized depending on the desired configuration. The data store can comprise a snapshot of the corresponding database contents as of the last system savepoint. The snapshot provides a read-only static view of the database as it existed as of the point (i.e., time, etc.) at which it was created. Uncommitted transactions, at such time, are not reflected in the snapshot and are rolled back (i.e., are undone, etc.). Database snapshots operate at the data-page level such that all pages being modified are copied from the source data volume to the snapshot prior to their being modified via a copy-on-write operation. The snapshot can store such original pages thereby preserving the data records as they existed when the snapshot was created.

System savepoints (also known in the field of relational database servers as checkpoints) can be periodically or manually generated and provide a point at which the recovery log can be truncated. The savepoint can, in some variations, include an undo log of transactions which were open in the savepoint and/or a cleanup log of transactions which were committed in the savepoint but not yet garbage collected (i.e., data which has been deleted by these transactions has been marked as deleted but has not been deleted in a physical manner to assure multiversion concurrency control).

The recovery log can comprise a log of all changes to the database system 105 since the last system savepoint, such that when a database server is restarted, its latest state is restored by replaying the changes from the recovery log on top of the last system savepoint. Typically, in a relational database system, the previous recovery log is cleared whenever a system savepoint occurs, which then starts a new, empty recovery log that will be effective until the next system savepoint. While the recovery log is processed, a new cleanup log is generated which needs to be processed as soon as the commit is replayed to avoid a growing data area because of deleted but not garbage collected data.

As part of a database system recovery/restart, after the savepointed state of data is restored, and before processing of the recovery log commences, all cleanup logs can be iterated through and, in implementations using a history manager, passed to the history manager for asynchronous garbage collection processing.

In addition, it can be checked if there are older versions of the cleanup log present in the savepoint which need to be processed synchronously with regard to the recovery log. In such cases, recovery log processing can wait until garbage collection of old versions of cleanup logs finish. However, recovery log processing can commence when there are newer versions of cleanup logs for garbage collection. In cases in which no old versions of cleanup logs exist, recovery log replay can start immediately after the cleanup log from the savepoint has been passed to the history manager.

A typical savepoint can have three phases. First, in the pre-critical phase all modified pages in the relational stores 332 (which are loaded into memory) can be iterated through and flushed to the physical persistence disk storage 348. Second, a critical phase can block all parallel updates to pages in the relational stores 332 and trigger all the remaining I/O for the physical persistence disk storage 348 to ensure the consistent state of data. Remaining I/O in this context can include I/O required for all pages that are still modified when entering the critical phase. Lastly, a post-critical phase can wait for all remaining I/O associated with the physical persistence disk storage 348.

For normal pages, page modifications must be synchronized with the savepoint. That means, that no page modifications are possible during critical phase of the savepoint and the savepoint critical section needs to wait for all current modifications to be finished. Technically a read-write-lock is used for that synchronization: the modifications acquire the shared-(read)-lock, while the critical phase acquires the exclusive-(write)-lock. Such synchronization is not necessary for temporary pages, as these pages are deleted implicitly with the next restart. By avoiding that synchronization, blocking savepoints can be avoided and coding which modifies temporary pages does not need to care about how long page modification lasts.

The relational stores 332, the temporary results 340, and/or the non-relational data store 342 may utilize temporary pages for a variety of database operations (e.g., encapsulating temporary or intermediate results for online operation, etc.). These temporary pages can be flushed from in-memory to the physical persistence disk storage 348 in case of memory shortages (i.e., when available main memory is below a pre-defined threshold, etc.). The temporary pages are deleted or otherwise not made available in case the database system 105 restarts.

The temporary pages can include a separate converter such that, in the critical phase, modifications can be made to such temporary pages while, at the same time, modifications cannot be made to non-temporary pages (i.e., pages that are not identified or otherwise categorized as temporary pages). The converter, in this regard, is a transient object that is linked to a particular temporary page which stores data for handling the temporary page (e.g., a page to handle intermediate results generated during query processing, etc.) and which is not persisted.

The converter can include a flag that indicates that the corresponding page is temporary in nature. The converter for the temporary pages are different and separate from the converters for non-temporary pages. The converters are not written or otherwise flushed to the physical persistent disk storage 348 and, as a result, the temporary pages cannot be recovered using such converter as part of the restart of the database system 105. This arrangement, in effect, makes the temporary pages not available upon the restart of the database system 105.

The temporary pages can be allocated using various mechanisms. Temporary pages can be allocated using a temp-pageaccess which is one instance of the PageAccess-class. There is a one-to-one relationship between pageaccesses and converter. The converter is never used directly but the pageaccess uses the converter to allocate a logical page number. The page and its controlblock can be allocated by the pageaccess. Upon allocation, the corresponding control block for such temporary page can be flagged as “temporary”. This flag indicates that modifications can be done to such temporary page without acquiring a consistent change. Not acquiring a consistent change will prohibit modification to the temporary page being blocked by the savepoint, but more important, operations on temporary pages will not block the savepoint.

FIG. 4 is a process flow diagram in which, at 410, a temporary page is allocated in main memory of an in-memory database in which pages are loaded into main memory and having associated physical disk storage. The temporary page is also flagged as being temporary. Subsequently, at 420, a savepoint is initiated for the database. During the savepoint, at 430, the temporary page is modified without acquiring a consistent change while, at the same time, other non-temporary pages are prevented from being modified. Later, at 440, the savepoint is finalized to enable the database to be rolled back to a point in time corresponding to the savepoint as part of a recovery process.

One or more aspects or features of the subject matter described herein can be realized in digital electronic circuitry, integrated circuitry, specially designed application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) computer hardware, firmware, software, and/or combinations thereof. These various aspects or features can include implementation in one or more computer programs that are executable and/or interpretable on a programmable system including at least one programmable processor, which can be special or general purpose, coupled to receive data and instructions from, and to transmit data and instructions to, a storage system, at least one input device, and at least one output device. The programmable system or computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other.

These computer programs, which can also be referred to as programs, software, software applications, applications, components, or code, include machine instructions for a programmable processor, and can be implemented in a high-level procedural language, an object-oriented programming language, a functional programming language, a logical programming language, and/or in assembly/machine language. As used herein, the term “computer-readable medium” refers to any computer program product, apparatus and/or device, such as for example magnetic discs, optical disks, memory, and Programmable Logic Devices (PLDs), used to provide machine instructions and/or data to a programmable processor, including a computer-readable medium that receives machine instructions as a computer-readable signal. The term “computer-readable signal” refers to any signal used to provide machine instructions and/or data to a programmable processor. The computer-readable medium can store such machine instructions non-transitorily, such as for example as would a non-transient solid-state memory or a magnetic hard drive or any equivalent storage medium. The computer-readable medium can alternatively or additionally store such machine instructions in a transient manner, for example as would a processor cache or other random access memory associated with one or more physical processor cores.

FIG. 5 is a diagram 500 illustrating a sample computing device architecture for implementing various aspects described herein. A bus 504 can serve as the information highway interconnecting the other illustrated components of the hardware. A processing system 508 labeled CPU (central processing unit) (e.g., one or more computer processors/data processors at a given computer or at multiple computers), can perform calculations and logic operations required to execute a program. A non-transitory processor-readable storage medium, such as read only memory (ROM) 512 and random access memory (RAM) 516, can be in communication with the processing system 508 and can include one or more programming instructions for the operations specified here. Optionally, program instructions can be stored on a non-transitory computer-readable storage medium such as a magnetic disk, optical disk, recordable memory device, flash memory, or other physical storage medium.

In one example, a disk controller 548 can interface one or more optional disk drives to the system bus 504. These disk drives can be external or internal floppy disk drives such as 560, external or internal CD-ROM, CD-R, CD-RW or DVD, or solid state drives such as 552, or external or internal hard drives 556. As indicated previously, these various disk drives 552, 556, 560 and disk controllers are optional devices. The system bus 504 can also include at least one communication port 520 to allow for communication with external devices either physically connected to the computing system or available externally through a wired or wireless network. In some cases, the communication port 520 includes or otherwise comprises a network interface.

To provide for interaction with a user, the subject matter described herein can be implemented on a computing device having a display device 540 (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information obtained from the bus 504 to the user and an input device 532 such as keyboard and/or a pointing device (e.g., a mouse or a trackball) and/or a touchscreen by which the user can provide input to the computer. Other kinds of input devices 532 can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback by way of a microphone 536, or tactile feedback); and input from the user can be received in any form, including acoustic, speech, or tactile input. In the input device 532 and the microphone 536 can be coupled to and convey information via the bus 504 by way of an input device interface 528. Other computing devices, such as dedicated servers, can omit one or more of the display 540 and display interface 514, the input device 532, the microphone 536, and input device interface 528.

To provide for interaction with a user, the subject matter described herein can be implemented on a computer having a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to the user and a keyboard and a pointing device (e.g., a mouse or a trackball) and/or a touchscreen by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user can be received in any form, including acoustic, speech, or tactile input.

In the descriptions above and in the claims, phrases such as “at least one of” or “one or more of” may occur followed by a conjunctive list of elements or features. The term “and/or” may also occur in a list of two or more elements or features. Unless otherwise implicitly or explicitly contradicted by the context in which it is used, such a phrase is intended to mean any of the listed elements or features individually or any of the recited elements or features in combination with any of the other recited elements or features. For example, the phrases “at least one of A and B;” “one or more of A and B;” and “A and/or B” are each intended to mean “A alone, B alone, or A and B together.” A similar interpretation is also intended for lists including three or more items. For example, the phrases “at least one of A, B, and C;” “one or more of A, B, and C;” and “A, B, and/or C” are each intended to mean “A alone, B alone, C alone, A and B together, A and C together, B and C together, or A and B and C together.” In addition, use of the term “based on,” above and in the claims is intended to mean, “based at least in part on,” such that an unrecited feature or element is also permissible.

The subject matter described herein can be embodied in systems, apparatus, methods, and/or articles depending on the desired configuration. The implementations set forth in the foregoing description do not represent all implementations consistent with the subject matter described herein. Instead, they are merely some examples consistent with aspects related to the described subject matter. Although a few variations have been described in detail above, other modifications or additions are possible. In particular, further features and/or variations can be provided in addition to those set forth herein. For example, the implementations described above can be directed to various combinations and subcombinations of the disclosed features and/or combinations and subcombinations of several further features disclosed above. In addition, the logic flows depicted in the accompanying figures and/or described herein do not necessarily require the particular order shown, or sequential order, to achieve desirable results. Other implementations may be within the scope of the following claims. 

What is claimed is:
 1. A method implemented by one or more data processors forming part of at least one computing device, the method comprising: allocating, in an in-memory database in which pages are loaded into main memory and having associated physical disk storage, a temporary page in the main memory; flagging the temporary page in the main memory as temporary, wherein the flagging indicates that the temporary page can be modified without acquiring a consistent change; after flagging the temporary page, initiating a savepoint for the database; subsequent to initiating the savepoint, entering a critical phase by the savepoint; modifying, during the critical phase of the savepoint, the temporary page without acquiring a consistent change while preventing other pages loaded into the main memory that are not flagged as being temporary from being modified; and finalizing the savepoint to enable the database to be rolled back to a point in time corresponding to the savepoint as part of a recovery process.
 2. A system comprising: at least one data processor; and memory storing instructions which, when executed by the at least one data processor, result in operations comprising: allocating, in an in-memory database in which pages are loaded into main memory and having associated physical disk storage, a temporary page in the main memory; flagging the temporary page in the main memory as temporary, wherein the flagging indicates that the temporary page can be modified without acquiring a consistent change; after flagging the temporary page, initiating a savepoint for the database; subsequent to initiating the savepoint, entering a critical phase by the savepoint; modifying, during a critical phase of the savepoint, the temporary page without acquiring a consistent change while preventing other pages loaded into the main memory that are not flagged as being temporary from being modified; and finalizing the savepoint to enable the database to be rolled back to a point in time corresponding to the savepoint as part of a recovery process.
 3. An in-memory database system comprising: main memory into which data is loaded for database operations; physical persistence disk storage; at least one data processor; memory storing instructions which, when executed by the at least one data processor, result in operations comprising: allocating a temporary page in the main memory; flagging a control block associated with the temporary page indicating that it is temporary, wherein the flagging indicates that the temporary page can be modified without acquiring a consistent change; after flagging the temporary page, initiating a savepoint, wherein the savepoint comprises (i) a pre-critical phase during which all modified pages loaded into the main memory are iterated through and flushed to the physical persistence disk storage, (ii) a critical phase during which parallel updates to pages in the main memory are blocked and remaining I/O for the physical persistence disk storage is triggered, and (iii) a post-critical phase during which all remaining I/O associated with the physical persistence disk storage is completed; subsequent to initiating the savepoint, entering the critical phase by the savepoint; modifying, during the critical phase of the savepoint, the temporary page without acquiring a consistent change while preventing other pages loaded into the main memory that are not flagged as being temporary from being modified; and finalizing the savepoint to enable the database to be rolled back to a point in time corresponding to the savepoint as part of a recovery process.
 4. The method of claim 1, wherein the flagging is performed prior to the initiation of the savepoint.
 5. The method of claim 1, wherein the flagging is performed subsequent to the initiation of the savepoint.
 6. The method of claim 1, wherein the flagging of the temporary page comprises flagging a control block associated with the temporary page indicating that it is temporary.
 7. The method of claim 1 further comprising: flushing the temporary page to the associated physical disk storage when an amount of free memory in the main memory is below a pre-defined level.
 8. The method of claim 1, wherein the temporary page is allocated by temp-pageaccess.
 9. The system of claim 2, wherein the flagging is performed prior to the initiation of the savepoint.
 10. The system of claim 2, wherein the flagging is performed subsequent to the initiation of the savepoint.
 11. The system of claim 2, wherein the flagging of the temporary page comprises flagging a control block associated with the temporary page indicating that it is temporary.
 12. The system of claim 2, wherein the operations further comprise: flushing the temporary page to the associated physical disk storage when an amount of free memory in the main memory is below a pre-defined level.
 13. The system of claim 2, wherein the temporary page is allocated by temp-pageaccess.
 14. The system of claim 3, wherein the control block is a transient object loaded into the main memory and not physically persisted in the associated physical disk storage.
 15. The system of claim 14, wherein the operations further comprise: deleting the temporary page after a restart of the database system.
 16. The method of claim 6, wherein the control block is a transient object loaded into the main memory and not physically persisted in the associated physical disk storage.
 17. The system of claim 11, wherein the control block is a transient object loaded into the main memory and not physically persisted in the associated physical disk storage.
 18. The method of claim 16 further comprising: deleting the temporary page after a restart of the database system.
 19. The system of claim 17, wherein the operations further comprise: deleting the temporary page after a restart of the database system. 